Low-altitude detection radar circuit board made of PPO material and preparation method of low-altitude detection radar circuit board

Abstract

The invention relates to the technical field of wireless communication and national security and protection, in particular to a low-altitude detection radar circuit board made of a PPO material and a preparation method thereof, and the circuit board comprises a PPO substrate layer, a metal circuit layer, an electromagnetic shielding layer, a heat dissipation enhancement layer and a solder mask protection layer. A chemical copper plating combination layer is arranged between the PPO base material layer and the metal circuit layer, and an electromagnetic shielding layer is clamped between the PPO base material layer and the heat dissipation enhancement layer; and the solder mask protection layer covers the surface of the metal circuit layer. Through the improvement of the structural design and the preparation process, the high temperature resistance is remarkably improved, the dielectric property is optimized, the signal transmission efficiency is improved, and the damp-heat aging resistance is enhanced.

Description

Technical Field

[0001] This invention relates to the fields of wireless communication and national defense security technology, and in particular to a low-altitude detection radar circuit board made of PPO material and its manufacturing method. Background Technology

[0002] Low-altitude detection radar is a core piece of equipment in fields such as low-altitude security, national defense, and drone countermeasures. Circuit boards, as the core component for signal acquisition, processing, transmission, and control, play a crucial role in connecting various electronic components and ensuring stable transmission of high-frequency signals. Currently, the substrate for electronic device circuit boards is primarily epoxy resin FR-4. This type of material, reinforced with fiberglass cloth, features mature processing technology, low cost, and good insulation properties, and is widely used in conventional electronic equipment; this is a well-known technology in this field.

[0003] The current mainstream technology for low-altitude sounding radar circuit boards is a multilayer circuit board using FR-4 epoxy resin substrate. Its structure mainly includes an epoxy resin substrate layer, a copper circuit layer, and a solder mask layer. Some high-end products may add a simple shielding coating. The manufacturing process is as follows: fiberglass cloth and epoxy resin composite molding substrate → drilling → hole wall metallization → photolithography etching to form circuits → solder mask coating → component soldering and assembly. The core feature of this technology is its reliance on the insulation and mechanical support capabilities of the FR-4 substrate to achieve signal transmission functionality through traditional PCB manufacturing processes.

[0004] However, existing technical solutions are not specifically designed for the extreme operating environment of low-altitude detection radar, resulting in the following technical defects: First, insufficient high-temperature resistance. The long-term operating temperature of the FR-4 substrate is only 80-100℃. When the low-altitude detection radar is working, the electronic components generate dense heat, and the circuit board temperature easily exceeds 100℃, leading to thermal deformation of the substrate, degradation of dielectric properties, and signal transmission distortion. Second, poor dielectric properties. FR-4 has a high dielectric constant and dielectric loss tangent in high-frequency scenarios ranging from hundreds of MHz to several GHz, resulting in large high-frequency signal transmission delay and severe energy loss, affecting radar detection accuracy and response speed. Third, weak resistance to humid heat aging. The FR-4 substrate is highly hygroscopic and easily absorbs moisture in high-humidity environments, leading to decreased insulation performance and corrosion of metal circuits. After long-term use, it is prone to faults such as solder joint detachment and short circuits. Fourth, low heat dissipation efficiency. The thermal conductivity of FR-4 is only 0.15-0.2 W / (m·K), making it difficult to quickly conduct the heat generated by the components, easily causing local overheating, affecting component life and circuit performance. Therefore, in order to better solve the above problems, this invention proposes a low-altitude detection radar circuit board made of PPO material and its manufacturing method. Summary of the Invention

[0005] To address the above issues, this invention proposes a low-altitude detection radar circuit board made of PPO material and its fabrication method, comprising a PPO substrate layer, a metal circuit layer, an electromagnetic shielding layer, a heat dissipation enhancement layer, and a solder resist protective layer; a chemically plated copper bonding layer is provided between the PPO substrate layer and the metal circuit layer, and an electromagnetic shielding layer is sandwiched between the PPO substrate layer and the heat dissipation enhancement layer; the solder resist protective layer covers the surface of the metal circuit layer. This invention better solves the problems of insufficient high-temperature resistance, poor dielectric properties, reduced signal transmission efficiency, weak resistance to damp heat aging, and low heat dissipation efficiency.

[0006] A low-altitude detection radar circuit board made of PPO material includes a PPO substrate layer, a metal circuit layer, an electromagnetic shielding layer, a heat dissipation enhancement layer, and a solder resist protective layer; a chemical copper plating bonding layer is provided between the PPO substrate layer and the metal circuit layer, and an electromagnetic shielding layer is sandwiched between the PPO substrate layer and the heat dissipation enhancement layer; the solder resist protective layer covers the surface of the metal circuit layer.

[0007] Furthermore, the PPO substrate layer is a 30% by mass glass fiber reinforced modified PPO material, and the thickness of the PPO substrate layer is 0.8-1.2 mm; Furthermore, the electromagnetic shielding layer adopts a composite structure of nickel-plated copper foil and PPO adhesive layer, and the electromagnetic shielding thickness is 50-80μm; Furthermore, the heat dissipation enhancement layer is a 20% by mass alumina-filled modified PPO material, and the thickness of the heat dissipation enhancement layer is 0.5-0.8 mm; Furthermore, the solder resist protective layer uses high-temperature resistant halogen-free solder resist ink, the thickness of the solder resist protective layer is 20-30μm, the solder joint area of ​​the metal circuit layer is provided with a 0.5-1.0μm thick immersion gold layer, and the thickness of the metal circuit layer is 35-70μm; Furthermore, the PPO substrate layer is provided with vias, the via diameter is 0.3-0.8mm, the via wall is provided with a 5-8μm electroless copper plating layer and a 20-30μm electroplated copper thickening layer, the vias penetrate the metal circuit layer to realize multi-layer circuit conduction; A method for fabricating a low-altitude detection radar circuit board made of PPO material includes the following steps: Step S1: Material pretreatment: Select the PPO resin and its additives with the corresponding formula, and prepare modified PPO granules by melt blending at 290-310℃ using a twin-screw extruder. Then, extrude and press the modified PPO granules into sheets of the corresponding thickness and vacuum dry at 120℃ for 4 hours. Step S2: Drilling and Metallization: Use a CNC drilling machine to process through holes on the PPO substrate. The drilling speed is controlled at 30,000-40,000 r / min. After deburring and chemical roughening the through holes, chemically plate copper in a 45-55℃ plating bath for 20-30 min to form a 5-8μm copper layer. Then electroplate copper to thicken it to 20-30μm. Step S3: Metal circuit fabrication: Coat the PPO substrate surface with photoresist, expose and develop to form a circuit pattern, etch with an acidic etch solution at 30-35℃ for 10-15 minutes to remove excess copper layer, peel off the photoresist and clean and dry. Step S4: Composite of shielding layer and heat dissipation layer: Composite a shielding layer material of the corresponding type on one side of the metal circuit layer, and fix it by hot pressing at 200-220℃ and 0.8-1.0MPa for 30-40s; Composite a heat dissipation layer material of the corresponding type on the other side of the substrate layer, using the same hot pressing parameters; Step S5: Solder resist and surface treatment: High-temperature halogen-free solder resist ink is coated on the surface of the metal circuit layer using screen printing process, cured at 150℃ for 60 minutes, and the solder joint area is subjected to immersion gold treatment. Step S6: Component Soldering and Inspection: Electronic components are soldered using reflow soldering. The reflow soldering temperature profile is as follows: preheating zone 150-180℃ for 60-90s, heating zone 180-220℃ for 30-40s, peak temperature 240-250℃ for 10-15s, cooling zone ≤100℃ for 60s. Electrical performance and appearance are inspected after soldering.

[0008] Furthermore, in step S1, when preparing the modified PPO particles for the circuit board, the additives are 30% glass fiber reinforcement, 20% alumina heat dissipation filler and 5% compatibilizer, and the thickness of the extruded PPO substrate is 0.8-1.2 mm. Furthermore, in step S4, the shielding layer material is a composite structure of stainless steel foil and PPO adhesive layer, the heat dissipation layer material is aluminum nitride-filled modified PPO material, a high-temperature solder with a melting point of 260°C is used for welding, and the peak temperature of reflow soldering is controlled at 250°C and held for 15 seconds.

[0009] Compared with the prior art, the significant advantages of this invention are: Significantly improved high-temperature resistance: This invention uses a glass fiber and alumina composite modified PPO material as the substrate. PPO resin itself has excellent high-temperature resistance. After modification with 30% glass fiber reinforcement, the long-term operating temperature can be stabilized above 120℃, effectively avoiding thermal deformation and dielectric property degradation of the substrate under high-temperature conditions, and solving the defect of insufficient high-temperature resistance of existing FR-4 substrates. The stainless steel foil shielding layer, aluminum nitride-filled heat dissipation layer and high-temperature solder used in extreme high-temperature scenarios can meet the short-term use requirements above 150℃. Optimized dielectric properties and improved signal transmission efficiency: The modified PPO substrate has a dielectric constant as low as 2.58 and a dielectric loss tangent significantly lower than FR-4. In high-frequency scenarios, it can significantly reduce signal transmission delay and energy loss. Combined with optimized via structure and circuit design, it further improves signal transmission integrity and significantly enhances the detection accuracy and response speed of low-altitude radar. Enhanced resistance to damp heat aging: PPO material itself has extremely low moisture absorption. After composite modification, its resistance to damp heat is further improved. It can maintain stable insulation performance in high humidity environments, effectively inhibit metal circuit corrosion, reduce faults such as solder joint detachment and circuit short circuits, extend the service life of circuit boards, and adapt to complex and humid outdoor working environments. Attached Figure Description

[0010] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart illustrating the fabrication process of a low-altitude detection radar circuit board made of PPO material and its fabrication method according to the present invention. Specific embodiments The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0011] A low-altitude detection radar circuit board made of PPO material includes a PPO substrate layer, a metal circuit layer, an electromagnetic shielding layer, a heat dissipation enhancement layer, and a solder resist protective layer; a chemical copper plating bonding layer is provided between the PPO substrate layer and the metal circuit layer, and an electromagnetic shielding layer is sandwiched between the PPO substrate layer and the heat dissipation enhancement layer; the solder resist protective layer covers the surface of the metal circuit layer.

[0012] In a specific embodiment, the PPO substrate layer uses 30% by mass glass fiber reinforced modified PPO material, which is made by melt blending of base PPO resin (melting point 285-325℃, dielectric constant 2.58), 30% glass fiber reinforcer, 20% alumina heat dissipation filler and 5% compatibilizer. The thickness is controlled at 0.8-1.2mm. Its core functions are to provide mechanical support, insulation and basic signal transmission. The mechanical strength and thermal stability are improved by glass fiber reinforcement, while maintaining low dielectric properties.

[0013] The metal circuit layer is made of oxygen-free copper with a thickness of 35-70μm and a line width / spacing of ≥0.1mm / 0.1mm. Its core function is high-frequency signal transmission and electrical connection of components. It is attached to the surface of the PPO substrate layer and is connected to other circuit layers through vias. The solder joint area is provided with a 0.5-1.0μm thick immersion gold layer to improve soldering compatibility and oxidation resistance.

[0014] The electromagnetic shielding layer adopts a composite structure of nickel-plated copper foil and PPO adhesive layer with a thickness of 50-80μm. Its core functions are electromagnetic interference shielding and signal crosstalk reduction. It is sandwiched between the PPO substrate layer and the heat dissipation enhancement layer. The PPO adhesive layer ensures compatibility and adhesion with the substrate layer and avoids delamination. For extreme high temperature scenarios, a composite structure of stainless steel foil and PPO adhesive layer can also be used to improve high temperature resistance.

[0015] Heat dissipation enhancement layer: Utilizes 20% alumina-filled modified PPO material with a thickness of 0.5-0.8mm. Its core function is to improve thermal conductivity and dissipate heat quickly. It is composited on the side of the electromagnetic shielding layer away from the PPO substrate layer, achieving indirect heat conduction with the metal circuit layer. This can increase the thermal conductivity of the PPO substrate from 0.28 W / (m·K) to 0.45 W / (m·K). For extreme high-temperature scenarios, aluminum nitride-filled modified PPO material can be used, increasing the thermal conductivity to over 0.6 W / (m·K).

[0016] Solder resist protective layer: Made of high temperature resistant halogen-free solder resist ink, with a thickness of 20-30μm. Its core function is to provide insulation protection and prevent circuit oxidation. It covers the surface of the metal circuit layer except for the solder joints.

[0017] Via structure: Vias are provided on the PPO substrate layer. The via diameter is 0.3-0.8mm. The via wall is provided with a 5-8μm electroless copper plating layer and a 20-30μm electroplated copper thickening layer. The via penetrates the metal circuit layer to realize multi-layer circuit conduction and ensure the continuity of signal transmission.

[0018] A method for fabricating a low-altitude detection radar circuit board made of PPO material includes the following steps: Step S1: Material pretreatment: Select the PPO resin and its additives with the corresponding formula, and prepare modified PPO granules by melt blending at 290-310℃ using a twin-screw extruder. Then, extrude and press the modified PPO granules into sheets of the corresponding thickness and vacuum dry at 120℃ for 4 hours. Step S2: Drilling and Metallization: Use a CNC drilling machine to process through holes on the PPO substrate. The drilling speed is controlled at 30,000-40,000 r / min. After deburring and chemical roughening the through holes, chemically plate copper in a 45-55℃ plating bath for 20-30 min to form a 5-8μm copper layer. Then electroplate copper to thicken it to 20-30μm. Step S3: Metal circuit fabrication: Coat the PPO substrate surface with photoresist, expose and develop to form a circuit pattern, etch with an acidic etch solution at 30-35℃ for 10-15 minutes to remove excess copper layer, peel off the photoresist and clean and dry. Step S4: Composite of shielding layer and heat dissipation layer: Composite a shielding layer material of the corresponding type on one side of the metal circuit layer, and fix it by hot pressing at 200-220℃ and 0.8-1.0MPa for 30-40s; Composite a heat dissipation layer material of the corresponding type on the other side of the substrate layer, using the same hot pressing parameters; Step S5: Solder resist and surface treatment: High-temperature halogen-free solder resist ink is coated on the surface of the metal circuit layer using screen printing process, cured at 150℃ for 60 minutes, and the solder joint area is subjected to immersion gold treatment. Step S6: Component Soldering and Inspection: Electronic components are soldered using reflow soldering. The reflow soldering temperature profile is as follows: preheating zone 150-180℃ for 60-90s, heating zone 180-220℃ for 30-40s, peak temperature 240-250℃ for 10-15s, cooling zone ≤100℃ for 60s. Electrical performance and appearance are inspected after soldering.

[0019] In specific embodiments, such as Figure 1 As shown, a method for fabricating a low-altitude detection radar circuit board made of PPO material includes the following steps: Step S1: Material pretreatment: Select base PPO resin (melting point 285-325℃, dielectric constant 2.58), add 30% glass fiber reinforcer, 20% alumina heat dissipation filler and 5% compatibilizer by mass fraction, put it into a twin-screw extruder, melt blend at 290-310℃, and extrude to prepare modified PPO granules; feed the modified PPO granules into an extruder to press into 0.8-1.2mm thick sheets, place them in a vacuum drying oven at 120℃ for 4 hours to remove moisture.

[0020] Step S2: Drilling and Metallization: According to the design drawings of the low-altitude radar circuit board, a CNC drilling machine is used to process through holes with a diameter of 0.5mm on the dried PPO substrate. The drilling speed is set to 35000r / min to avoid cracking of the substrate. After deburring the through holes, a chemical roughening solution is used for roughening. Then, the substrate is immersed in a 48℃ chemical copper plating solution for 20-30 minutes to form a copper layer with a thickness of 5-8μm on the hole wall. Subsequently, an electroplating copper process is used to thicken the copper layer on the hole wall to 20-30μm to ensure the conductivity of the hole wall.

[0021] Step S3: Metal Line Fabrication: Coat the PPO substrate surface uniformly with photoresist, expose it according to the circuit pattern using a UV exposure machine, and expose the copper layer area to be etched after development with a developer; immerse the substrate in an acidic etching solution at 30-35℃ for 10-15 minutes to remove excess copper layer and form an oxygen-free copper circuit layer with line width / line spacing = 0.1mm / 0.1mm; finally, peel off the remaining photoresist, clean with deionized water, and dry.

[0022] Step S4: Composite shielding layer and heat dissipation layer: Lay a composite shielding material of nickel-plated copper foil and PPO adhesive layer on one side of the metal circuit layer, place it in a hot press, set the temperature to 210℃ and the pressure to 0.9MPa, and hot press for 35s to make the shielding layer and the substrate layer tightly bonded; Lay a 20% alumina-filled modified PPO heat dissipation plate on the other side of the substrate layer, and use the same hot pressing parameters (to carry out hot pressing composite to ensure that the composite structure is flat and free of bubbles).

[0023] Step S5: Solder resist and surface treatment: Apply high-temperature halogen-free solder resist ink to the surface of the metal circuit layer using screen printing process. The coating thickness is 20-30μm. Place it in a curing oven and cure at 150℃ for 60min. Perform immersion gold treatment on the solder joint area of ​​the circuit board, controlling the gold layer thickness to 0.5-0.8μm.

[0024] Step S6: Component Soldering and Inspection: Reflow soldering is used to solder the electronic components for low-altitude detection radar. The reflow soldering temperature profile is strictly controlled as follows: preheating zone 160-180℃ for 75s, heating zone 180-220℃ for 35s, peak temperature 245℃ for 12s, cooling zone ≤100℃ for 60s. After soldering, electrical continuity is tested with a multimeter, appearance defects are observed with a microscope, high and low temperature test chamber is used to test high temperature resistance, and damp heat test chamber is used to test damp heat resistance. Components that pass the tests are considered finished products.

[0025] This invention addresses the need for lightweight design by employing a structure of "PPO substrate layer + flexible metal circuit layer + ultra-thin shielding film," removing the heat dissipation enhancement layer, and optimizing the PPO substrate formula by adding 15% glass fiber reinforcement. While ensuring basic mechanical properties, the overall thickness of the circuit board is reduced to below 1.5mm, making it suitable for miniaturized low-altitude radar equipment.

[0026] This invention is designed for short-term use in extreme high-temperature environments, i.e., above 150°C. It uses a high-temperature modified PPO substrate with a glass transition temperature of 230°C, replaces the shielding layer with stainless steel foil, and uses aluminum nitride-filled modified PPO for the heat dissipation layer, increasing the thermal conductivity to 0.6 W / (m·K). The welding process uses high-temperature solder with a melting point of 260°C, meeting the high-temperature resistance requirements in special scenarios.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0029] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A low-flying detection radar circuit board of PPO material, characterized in that, The application relates to a PPO substrate layer, a metal circuit layer, an electromagnetic shielding layer, a heat dissipation enhancement layer and a solder resist protective layer; a chemical copper plating bonding layer is arranged between the PPO substrate layer and the metal circuit layer, and the electromagnetic shielding layer is arranged between the PPO substrate layer and the heat dissipation enhancement layer; and the solder resist protective layer covers the surface of the metal circuit layer.

2. The PPO material low-altitude detection radar circuit board according to claim 1, wherein, The PPO substrate layer is a 30% mass fraction glass fiber reinforced modified PPO material, and the thickness of the PPO substrate layer is 0.8-1.2 mm.

3. The PPO material low-altitude detection radar circuit board according to claim 1, characterized in that, The electromagnetic shielding layer adopts a composite structure of a nickel-plated copper foil and a PPO adhesive layer, and the thickness of the electromagnetic shielding layer is 50-80 mu m.

4. The PPO material low-altitude detection radar circuit board according to claim 1, characterized in that, The heat dissipation enhancement layer is a 20% mass fraction alumina filled modified PPO material, and the thickness of the heat dissipation enhancement layer is 0.5-0.8 mm.

5. The PPO material low-altitude detection radar circuit board according to claim 1, characterized in that, The solder resist protective layer adopts high-temperature-resistant halogen-free solder resist ink, the thickness of the solder resist protective layer is 20-30 mu m, the solder point area of the metal circuit layer is provided with a 0.5-1.0 mu m thick gold plating layer, and the thickness of the metal circuit layer is 35-70 mu m.

6. The PPO material low-altitude detection radar circuit board according to claim 1, wherein, A via hole is arranged on the PPO substrate layer, the via hole has a diameter of 0.3-0.8 mm, the hole wall is provided with a 5-8 mu m chemical copper plating layer and a 20-30 mu m electroplated copper thickening layer, and the via hole penetrates through the metal circuit layer to realize multi-layer circuit conduction.

7. A method for manufacturing a PPO material low-altitude detection radar circuit board, characterized in that, The application further discloses a preparation method of the PPO substrate layer. Step S1: material pretreatment: selecting a corresponding formula PPO resin and its additives, preparing modified PPO particles by melt blending of the PPO resin and the additives in a double-screw extruder at 290-310 DEG C, and then extruding and pressing the modified PPO particles into a plate with a corresponding thickness and vacuum drying the plate at 120 DEG C for 4 hours; Step S2: drilling and metallization: processing a via hole on the PPO substrate plate by using a numerical control drilling machine, controlling the drilling speed at 30000-40000 r / min, deburring the via hole, chemically roughening the via hole, and then chemically plating copper in a 45-55 DEG C plating solution for 20-30 min to form a 5-8 mu m copper layer and then electroplating copper to 20-30 mu m; Step S3: metal circuit preparation: coating a photoresist on the surface of the PPO substrate, forming a circuit pattern through exposure and development, etching the excess copper layer by using a 30-35 DEG C acidic etching liquid for 10-15 min, and then cleaning, peeling off the photoresist and drying; Step S4: shielding layer and heat dissipation layer compounding: compounding a corresponding type of shielding layer material on one side of the metal circuit layer, fixing by hot pressing at 200-220 DEG C and 0.8-1.0 MPa for 30-40 s, and compounding a corresponding type of heat dissipation layer material on the other side of the substrate layer by using the same hot pressing parameters; Step S5: solder resist and surface treatment: coating high-temperature-resistant halogen-free solder resist ink on the surface of the metal circuit layer by using a screen printing process, curing at 150 DEG C for 60 min, and performing gold plating treatment on the solder point area. Step S6: component soldering and testing: electronic components are soldered by reflow soldering process, the reflow soldering temperature curve is: preheating zone 150-180℃ for 60-90s, heating zone 180-220℃ for 30-40s, peak temperature 240-250℃ for 10-15s, cooling zone ≤100℃ for 60s, and electrical performance and appearance testing are performed after soldering.

8. The method for manufacturing a low-altitude detection radar circuit board made of PPO material according to claim 7, characterized in that, In step S1, when preparing the modified PPO particles of the circuit board, the additives are 30% glass fiber reinforcing agent, 20% aluminum oxide heat dissipation filler and 5% compatibilizer, and the thickness of the PPO substrate board extruded and pressed is 0.8-1.2mm.

9. A method for manufacturing a low-altitude detection radar circuit board made of PPO material according to claim 7, characterized in that, In step S4, the shielding layer material is a composite structure of stainless steel foil and PPO adhesive layer, the heat dissipation layer material is aluminum nitride filled modified PPO material, high temperature solder with a melting point of 260℃ is used for soldering, and the peak temperature of reflow soldering is controlled at 250℃ and maintained for 15s.

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